Trypanosoma cruzi primary infection prevents severe re-infection in mice

The effect of Trypanosoma cruzi re-inoculations on experimentally infected mice was evaluated. Mice received a primary infection by intradermal inoculation of 5x103 T. cruzi metacyclic infective forms from laboratory infected Rhodnius prolixus. From 200 mice initially infected, 52 survived the course of the infection during 23 weeks. From these, 45 mice were re-inoculated and seven used as infected control. Two re-inoculations were performed using the same conditions as in the prime-infection. Observations on re-inoculated mice revealed a parasitemia level lower than that detected during the primary-infection. Serologic evaluation showed no variation in the immunoglobulin profile, maintaining similar IgM and IgG levels after re-inoculations. Similar mortality rates were observed in primary-infected, re-inoculated and infected control mice. No remarkable histopathological changes attributable to re-inoculation were detected. These results lead us to conclude that T. cruzi re-inoculation in mice previously infected with the same parasite does not produce a reactivation of infection similar to the typical acute clinical or immunological profiles. This also suggests that T. cruzi primary infection may prevent severe re-infection, establishing a protective stage making infected mice resistant to a second infection. Epidemiological implications of the present findings are discussed.(AU) Se evalua el efecto de reinoculaciones por Trypanosoma cruzi en ratones experimentalmente infectados. De un total de 200 ratones que fueron infectados por via intradermica con un inoculo de 5x103 tripomastigotes metaciclicos provenientes de especimenes de Rhodnius prolixus, 52 sobrevivieron a la primo-infeccion luego de 23 semanas. De estos 45 fueron re-inoculados en la misma forma como en la infeccion primaria y siete fueron utilizados como controles infectados no re-inoculados. Observaciones sistematicas llevadas a cabo en muestras de los ratones re-inoculados revelaron parasitemias significativamente menores que las detectadas durante la primo-infeccion. La evaluacion serologica no mostro diferencias en los niveles de IgM e IgG entre ratones primo-infectados y los re-inoculados. Observaciones histopatologicas no mostraron cambios atribuibles al efecto de las re-inoculaciones en muestras de corazon y musculo esqueletico. Una tasa similar de mortalidad fue observada en ratones primo-infectados, re-inoculados y controles infectados. Se concluye que re-inoculaciones con T. cruzi en ratones previamente infectados con el mismo parasito no producen reactivacion de la infeccion similar al tipico cuadro agudo. Asimismo, se sugiere que la primo-infeccion por T. cruzi previene una reinfeccion severa estableciendo un estado de proteccion y resistencia a subsecuentes infecciones. Se discuten las implicaciones epidemiologicas de los presentes hallazgos.(AU)